It is quite common that multiple operators of cellular networks, often referred to as Public Land Mobile Networks (PLMNs), provide wireless communication services in the same geographical region by running their own networks “in parallel” using their own proprietary equipment, including base stations covering corresponding cells. In this way, each operator has full control of its services and resources when providing such services to their respective subscribers, while their coverage areas are at least partly overlapping.
In such a scenario, it is common that the operators' coverage areas include so-called “hot-spots”, which are usually limited areas with a high concentration of terminal users generating dense traffic which often results in congestion in a cell such that no further sessions can be admitted in the cell. This can be solved by adding a base station with relatively low output power to the existing network to provide an extra cell of small size and with additional capacity for radio communication. On the other hand, there may also be areas with deficient radio coverage where there is a need for coverage extension to avoid loss of radio contact with mobile terminals in those areas due to poor radio reception, which again can be solved by adding an extra base station to compensate for missing coverage in such an area.
When multiple network operators need to add an extra base station to provide additional coverage in basically the same area, for whatever reason, considerable costs and efforts can be saved by sharing the same base station instead of setting up one base station per operator to provide basically the same coverage. In this way, a plurality of such shared base stations may be employed by multiple operators to supplement their cellular networks wherever needed.
In the following, the term “radio node” will be used to generally represent a node providing radio coverage in one or more cells, which could be e.g. a base station, a Radio Network Controller (RNC) or an e-Node B, depending on the technology and terminology used. It should be noted that this description pertains to any technologies and communication standards where shared radio nodes can be employed, such as GSM, UMTS, LTE, etc. In some implementations, a shared radio node is connected to multiple core networks belonging to the respective operators, typically using an Iu interface connection to a Serving GPRS Support Node (SGSN) or Mobile Switching Centre (MSC), or an S1 interface/connection to a Mobility Management Entity (MME) in respective core networks. The above arrangement of employing a shared radio node by multiple operators and core networks is often referred to as “Multi-Operator Core Network” (MOCN). The shared radio node is also connected to the existing individual radio networks, e.g. using X2 connections such as in the case of E-UTRAN, in order to properly interact with each operator specific radio network, e.g. for handover signalling. Accordingly, the shared radio node must thus be configured to interact with all operator specific networks, i.e. both core and radio networks, in line with their specific requirements and used schemes.
However, it may be difficult for the individual operators to incorporate the shared radio node and its coverage in their existing cell structures and procedures which are typically configured by means of careful cell planning, among other things. Moreover, a cellular radio network is typically divided into so-called “tracking areas”, sometimes also termed “registration areas”, “location areas” or “paging areas”. In the following, the term “tracking area” will be used to represent any of the above expressions without limitation to any particular used technology. A tracking area typically includes a group of adjacent cells and can be of any suitable size, as determined by the operator to fit into an overall cell plan.
Such tracking areas are used to enable paging of mobile terminals based on e.g. tracking area update messages transmitted regularly from the terminals to the core network as they move from one tracking area to another in idle state. This type of message is often referred to as “Tracking Area Update Request” or TAU in LTE, or “Location Update” and “Routing Area Update” in GSM and in UMTS.
In this way, the core network can page a terminal for an incoming call by transmitting a paging message only in the cells of the terminal's latest reported tracking area. When entering a cell in idle state, the terminal can in turn determine whether it is necessary to update its tracking area to the core network by reading a Tracking Area Code, typically denoted TAC, being typically a numeric value which is regularly broadcasted along with other system information in each cell. That is, the terminal sends a new message for updating tracking area towards the core network when the terminal reads a TAC that is different since its previous transmitted tracking area update(s). In some implementations, the terminal maintains a so-called “Tracking Area (TA) list” with multiple TACs as provided from the core network, and when reading a broadcasted TAC not included in the TA list, the terminal initiates a tracking area update such that the serving radio node reports that TAC to the core network. Thereby, the core network knows the location of each terminal on a tracking area level, i.e. the core network knows that the terminal is likely located within one or a few known tracking areas.
As indicated above, when shared radio nodes are employed by multiple operators, their respective radio networks comprise a mix of dedicated and shared radio nodes which may be difficult to coordinate in a common radio network structure. The above TAC parameter is typically assigned to cells according to an operator specific scheme, in order to support an effective and logic paging procedure which is adapted to fit the tracking area plan of the operator's radio network.
In short, each operator has its own division of cells into tracking areas and the tracking area plan of one radio network differs from that of another radio network. Therefore, it is a problem that the TAC broadcasted by a shared radio node may not be very useful or fitting in the cell plan or tracking area plan of a particular operator specific radio network, and the operators must find solutions to bring about a compromise or conversion between a “shared” TAC and their operator specific tracking area plans. For example, a particular cell of a shared radio node may be comprised in a certain tracking area of one operator while the same cell may be comprised in an altogether different tracking area of another operator. If a cellular network includes multiple shared radio nodes in the range of, say, 50-100 it is a difficult and demanding task to plan tracking areas which must be coordinated with the other operators' networks.